Yggdrasil Resurrection Idea

Hi folks i have had a bit thinking about this and i wanted to know what you guys thought of it.You see im trying to think of ways to resurrect the dead god Yggdrasil the world tree/ the ash tree and so on.I am in a campaign running a combination of pathfinder mythos and dnd mythos so in this the world tree is dead as per normal (Killed by the spellplauge in dnd) and i want to try and give my Druidic moss lich a noble goal one greater than himself.

So far i have a few ideas but most of them come from resurrecting an evil dead god witch i figure would be vary different than resurrecting a good/true neutral deity.(Though he is all too willing to sacrifice himself for this goal if needed.Im planning for this ritual to encompass most if not all his life's work.

And do to the combining of the lore from dnd and pathfinder (Do to both having the multiverse theory) im trying to get ideas from both sides.

So any ideas? Side note i will be getting all the ideas i have and posting them here latter.

Oh also for those wondering why i chose Yggdrasil its because my druids a norse worshiping guy and yggdrasil was a prity important god to most of the cosmos so he figures bringing it back might help bigtime in lowering a bit of the chaos.